Salmonella enterica serovar Typhimurium (Salmonella Typhimurium) is one of the most common causes of enterocolitis in humans. Pathogenesis of this facultative intracellular pathogen is dependent on the ability to invade non-phagocytic cells, such as those found in the intestinal epithelium. Invasion is dependent on a type III secretion system (T3SS1), which is used to translocate a set of bacterial effector proteins into the host cell. Following internalization, intracellular Salmonella survive and replicate within a modified phagosome, the Salmonella-containing vacuole (SCV). A second type III system (T3SS2) is induced intracellularly and is associated with intracellular survival/replication and biogenesis of the SCV. We are currently using a primary human macrophage model system to dissect the roles of T3SS1 and T3SS2 in Salmonella-host cell interactions.